Re: ATM 3 or 4 vane spider

[doug kniffen <dk@usmo.com>]

At 03:00 PM 12/28/99 +0000, you wrote:
>If you offset the four support vanes by roughly half the radius of the
>secondary holder, you will see, instead of four very bright spikes, four
>slightly less bright primary spikes. This is a far more noticeable effect
>that the difference between 3 or 4 intersecting vanes. I have no optical
>explanation, only my experience and that of several other English ATM's.

Hi Chris,

I don't doubt what you describe, but I haven't tried it. Taking a guess at
it, it seems that the vane offset is enough to prevent stacking the spikes
without being enough to seperate them into eight spikes. Is there a
noticable increase spike width? I imagine that the decreased brightness
(from not stacking) makes the secondary (and tertiary?) spectrum faint
enough that spike length seems considerably shorter. Is this true too? Does
tensioning the vanes produce an "X" shape where the brightest part of the
spike is the middle of the length instead being next to the star? Maybe I
should try a few experiments with my SCT and some vane material.

Doug K